Food as Cause of Human Salmonellosis

Foodborne salmonellosis is still today a serious public health issue: very common in poor developing countries, due to the bad general hygiene conditions, it is also largely widespread in developed countries. In the latter, 95% of recorded clinical cases are foodborne (Liu et al., 2011). According to EFSA epidemiological data (2011), in the European Union (EU) Salmonella is the second cause of foodborne disease after Campylobacter and it is still first in many EU States, such as Italy. Unlike Campylobacter, Salmonella often cause very large multistate outbreaks of food infection; this proves the greater resistance of this pathogen in the external environment and in food. In developed countries the main source of salmonellosis is still today food of animal origin, particularly meat (fresh and processed) and shell eggs. Also fresh fruits and vegetables can convey the bacteria to humans, as well as undrinkable water. Salmonella is quite resistant to adverse conditions and this allows them to persist in the environment and spread along the food chain, from the animals to the food of animal origin, or to plants that are fertilized with animal manure. Two species are currently registered into the genus Salmonella: S. enterica and S. bongori. The former is better adapted than the latter to live in the intestine of man and warm-blooded animals, whereas S. bongori travels in the external environment and is detectable in the intestinal contents of warm-blooded animals, so it is rare for it to be found in food for human consumption. The dangers for human health mainly arise from food contaminated with Salmonella enterica, which is often present in the intestines of livestock and pets, without causing any infection to the animals (“healthy carrier” condition). Humans can be healthy carriers of S. enterica in the intestine too. This may be a potential hazard to food hygiene, if the healthy carriers are the people involved in producing and handling the food. Usually a healthy carrier eliminates Salmonella in their faeces for several months after the episode of gastroenteritis through which they became carrier. In the case of Salmonella ser. Typhi, however, it has been demonstrated that humans can be asymptomatic carriers of the bacterium for decades (Weill, 2009). The genus Salmonella has more than 2,500 serotypes, and over 1,600 of these are within the enterica species, but not all serotypes have the same affinity for human and/or animals and they are not all found in the food that humans consume. Some serotypes (Typhy, Paratyphi A and C, some clones of Paratyphi B and Sendai) travel almost exclusively among men, and express their pathogenicity only when they infect a human being. Few serotypes travel exclusively among animals and do not infect humans, if not seldom (e.g. Abortusovis in sheep and Gallinarum-Pullorum in poultry). On the contrary, approximately 150 serotypes travel more or less constantly between the animal reservoir, the environment, food and man, starting from Salmonella ser. Typhimurium. Some serotypes, however, have a particular preference for some animal species: Enteritidis, Hadar, Heidelberg, Saintpaul,